Shelf



FIG. 1 is a bottom right front perspective view of a shelf showing our new design;

FIG. 2 is a front elevational view thereof; the rear elevational view being a mirror image;

FIG. 3 is a top plan thereof;

FIG. 4 is a right side elevational view thereof; the left side elevational view being a mirror image; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a shelf, as shown and described. 